CRACKS IN SEA ICE AND THEIR EFFECT ON OPERATIONS
W. D. Kingery and R. L. Coble
In field operations, decisions must frequently be made concerning the extent that cracks limit the possibility of operating on sea ice. A few rules about effects of cracks are given by Assur in recommendations for aircraft operations on ice sheets (1). Only cracks greater than ⅟2 inch in width must be included in a survey of an area proposed for aircraft use; those over 1 ⅟2 inches wide are to be healed with slush. Assur also recommends that 10% greater ice thickness is required when cracks 1 to 2 inches wide are present; 30% greater thickness is required when wet open cracks are present. It is recommended that heavy loads not be parked on a crack nor allowed to pass over intersections of several cracks; parking is permitted at distances equal to the load influence radius from a crack or free edge.
There are various ways in which cracks are formed in ice and various sizes in which they occur. In discussions of their effect on sea ice strength, no quantitative analyses have been made. While, in the present chapter, we do not carry out a complete quantitative analysis, we develop a rational basis for estimating effects of cracks.
Cracks passing completely through the ice sheet have the most deleterious effect on load-bearing capacity. Open wet cracks can result from wind or tidal or wave action. Tidal cracks are frequently observed in shore-bound ice, occurring when tidal action lifts the ice sheet above or below the level at which it is shore- bound. Cracks tend to form parallel to the shore at a distance from the shore related to an "action radius" that depends on the